Method and apparatus for dimensionally measuring by means of coordinate measuring instruments

Abstract

A method and an apparatus for dimensionally measuring parts by means of a coordinate measuring instrument. In order enable measurement of parts that are made of different materials with great accuracy, a computerized tomography sensor is integrated into the coordinate measuring instrument.

The invention claimed is: 
     
       1. Method for dimensional measurement of a measuring object with a coordinate measuring device having an integrated computer tomography sensor,
 wherein measuring points to be chosen from all points measured with the computer tomography sensor are selected by the operator by selection of CAD-patches of a CAD-model of the measuring object. 
 
     
     
       2. Method according to  claim 1 , characterized in that the measurement of structures that are located inside the component to be measured, is carried out with computer tomography, the measurement of the component surface is carried out completely or partially by optical or tactile sensors and the measurement results of the two sensors are evaluated finally in a coordinate system. 
     
     
       3. Method according to  claim 1 , characterized in that the sensors used, that is the computer tomography sensor and the optical or tactile or laser line sensor, are mutually calibrated before the measurement with respect to calibration ranges. 
     
     
       4. Method according to  claim 1 , characterized in that the point clouds measured by tomography and a tactile or optical sensor, are mutually aligned or superposed, by means of optimal overlap of common geometry features, and thus a measurement within a coordinate system becomes possible. 
     
     
       5. Method according to  claim 1 , characterized in that the CAD model of the measured object and the measuring point cloud are made to overlap by BestFit or manual adaptation. 
     
     
       6. Method according to  claim 1 , characterized in that all the measuring points that are located within a search area about the chosen CAD patch are used for the further evaluation. 
     
     
       7. Method according to  claim 1 , characterized in that, in the case of the selection of individually measured points, additional points are automatically selected and added. 
     
     
       8. Method according to  claim 1 , characterized in that, before the selection of a point, a regular geometric element, such as, a cylinder/plane is selected as target element, and then as many measuring points are selected by the software as are needed, until the shape deviation of a compensation element of the type of the target element, which is calculated from the selected points, in its shape deviation falls below a previously established limit value. 
     
     
       9. Method according to  claim 1 , characterized in that, before the selection of a point, a cylinder is selected as regular geometric target element, and then as many measuring points are selected by the software as are needed, until the shape deviation of a compensation element, which is calculated from the selected points, in its shape deviation falls below a previously established limit value. 
     
     
       10. Method according to  claim 1 , characterized in that, before the selection of a point, a plane is selected as regular geometric target element, and then as many measuring points are selected by the software as are needed, until the shape deviation of a compensation element, which is calculated from the selected points, in its shape deviation falls below a previously established limit value. 
     
     
       11. Method according to  claim 1 , characterized in that, before the selection of a point, a sphere is selected as regular geometric target element, and then as many measuring points are selected by the software as are needed, until the shape deviation of a compensation element, which is calculated from the selected points, in its shape deviation falls below a previously established limit value. 
     
     
       12. Method according to  claim 1 , characterized in that, before the selection of a point, a torus is selected as regular geometric target element, and then as many measuring points are selected by the software as are needed, until the shape deviation of a compensation element, which is calculated from the selected points, in its shape deviation falls below a previously established limit value. 
     
     
       13. Method according to  claim 1 , characterized in that, before the selection of a point, a target element in the form of a free form patch described in the CAD format is selected, and then as many measuring points are selected by the software as are needed, until the shape deviation of a compensation element, which is calculated from the selected points, in its shape deviation falls below a previously established limit value. 
     
     
       14. Method according to  claim 1 , characterized in that the evaluation of measuring points measured with computer tomography is ensured by the simulation of a tactile or optical measurement on the point cloud. 
     
     
       15. Method according to  claim 1 , characterized in that, for correcting measurement errors in the tomography, the deviation between the tomographic measurement and the optical or tactile measurement is determined for a first sample part, and this deviation is then used for correcting the tomographic measurement results. 
     
     
       16. Method according to  claim 1 , characterized in that, the deviation value between tomographic and tactile or optical measurement is added in memory to the coordinates of the tactile or optical measuring points, and corrected during the later evaluation. 
     
     
       17. Method according to  claim 1 , characterized in that, in the evaluation of purely tomographically measured parts, the evaluation by simulation of a tactile or optical measurement on the computer tomography point cloud is carried out taking into account the measurement deviation between the tactile/optical and the tomographic measurement which was determined mathematically beforehand for each measuring point. 
     
     
       18. Method according to  claim 1 , characterized by
 step 1:
 measurement of a first measured object by means of computer tomography, 
 measurement of measuring points on the same measured object with tactile or optical sensor, 
 storage of the tactile/optical measuring point coordinates with the associated deviation between tactile/optical and tomographically determined measurement result, and 
 evaluation, 
 
 step 2:
 measurement of a second measured object with similar geometry by means of the tomographic sensor, 
 determination of simulated tactile or optical measuring points by selecting one or more tomography measuring points in the vicinity of the place which was stored for the tactile or optical measurement, 
 correction of the measurement result so obtained, by the measurement deviation determined in step 1 for the tactile measurement place, and 
 evaluation. 
 
 
     
     
       19. Method according to  claim 1 , characterized in that the evaluation of the measurement results is carried out by comparing the actual measurement values with the CAD target elements, and a color deviation representation. 
     
     
       20. Method according to  claim 1 , characterized in that the evaluation of the measurement results is carried out by determining measures, such as length, angle, diameter, distance, and comparison with the target values established in a drawing. 
     
     
       21. Method according to  claim 1 , characterized in that target values, the upper and lower tolerances, are taken from a CAD format. 
     
     
       22. Method according to  claim 1 , characterized in that, to record with X-ray tomography parts to be measured, part to be measured must be applied on spatially small-size contact points of a like-like structure. 
     
     
       23. Method according to  claim 1 , characterized in that the application structure with the knobs is manufactured as a plastic injection molded part. 
     
     
       24. Method according to  claim 1 , characterized in that, for the evaluation of the X-ray tomography, an erosion filter is used for separating the knob structures from the measured object proper. 
     
     
       25. Method according to  claim 1 , characterized in that, by means of an object size filter, only the largest measured object remains in the image, and thus the knob structures are erased. 
     
     
       26. Method according to  claim 1 , characterized in that the measurements are carried out on the remaining largest object. 
     
     
       27. Method according to  claim 1 , characterized in that the measured object and knob structure are connected by a thin adhesive film, for example one that is applied by spraying. 
     
     
       28. Coordinate measuring device for measuring an object ( 3 ,  28 ,  30 ,  32 ) with an X-ray sensor system as first sensor system comprising an X-ray radiation source ( 10 ,  42 ) and at least an X-ray radiation sensor that captures the X-rays ( 7 ,  56 ), as well as a second sensor system, such as a tactile and/or optical sensor system ( 8 ,  11 ;  9 ,  44 ,  46 ), is adapted for positioning in the x, y and/or z direction of the coordinate measuring device relative to the object, where the X-ray sensor system ( 7 ,  10 ,  42 ,  56 ) is adapted for positioning in accordance with the second sensor system ( 8 ,  11 ;  9 ,  44 ,  46 ) in the coordinate measuring device ( 10 ),
 wherein said object ( 28 ) consists of a core ( 20 ,  30 ) with a first density and an envelope ( 22 ,  32 ) with a second density, the first density is much higher than the second density, the core is measurable with the X-ray sensor system ( 7 ,  10 ,  42 ,  56 ), and the envelope with the second sensor system ( 8 ,  9 ,  11 ,  44 ,  46 ), and wherein the object to be measured ( 3 ,  28 ) is applied on spatially small-size contact points of a knob-like structure. 
 
     
     
       29. Coordinate measuring device according to  claim 28 , characterized in that the coordinate measuring device comprises an evaluation unit ( 34 ), in which the measurement results of the two sensors can be evaluated finally in a common coordinate system. 
     
     
       30. Coordinate measuring device according to  claim 28 , characterized in that the second sensor system ( 8 ,  46 ) is a laser line sensor. 
     
     
       31. Coordinate measuring device according to  claim 28 , characterized in that the second sensor system is a tactile sensor ( 9 ,  44 ). 
     
     
       32. Coordinate measuring device according to  claim 28 , characterized in that the application structure with the knobs is a plastic injection molded part. 
     
     
       33. Coordinate measuring device according to  claim 28 , characterized in that, for the evaluation of the X-ray tomography, an erosion filter for separating the knob structures from the measured object proper is provided. 
     
     
       34. Coordinate measuring device according to  claim 28 , characterized in that, due to the use of an object size filter, only the largest measured object remains in the image, and thus the knob structures are erased. 
     
     
       35. Coordinate measuring device according to  claim 28 , characterized in that the measurements can be carried out on the remaining largest object. 
     
     
       36. Coordinate measuring device according to  claim 28 , characterized in that the measured object and the knob structure are connected by a thin adhesive film, for example one that is applied by spraying.